Currently, the number of data networks and the volume of traffic these networks carry are increasing at an ever faster rate. The network devices making up these networks generally consist of specialized hardware designed to move data at very high speeds. Typical networks, such as Ethernet based networks, are mainly comprised of end stations, Ethernet hubs, switches, routers, bridges and gateways. ATM networks are constructed with similar network devices adapted to carry ATM traffic, e.g., ATM capable end stations, edge devices and ATM switches.
Voice traffic, on the other hand, is handled by networks comprised of different types of equipment. Currently, the topology of the telecommunications telephony network constitutes a combination of two main elements: switching products and transmission products. Switching products are defined within sets of hierarchies and include, for example, Class-X switches such as Class-4 and Class-5 switches. The lowest level in the hierarchy is the Class-5 switch (e.g., Lucent ESS-5) which is connected on the user side to either home telephones or Private Branch Exchanges (PBXs) within enterprises. On the network side, the Class-5 switch is connected via transmission equipment to a Class-4 switch. Class-4 switches are higher in the hierarchy and are connected to Class-3 switches through transmission equipment.
The transmission products are divided into two families: (1) Time Division Multiplexing (TDM) over Synchronous Optical Network (SONET)/Synchronous Data Hierarchy (SDH) networks and (2) TDM over Asynchronous Transfer Mode (ATM) over SONET/SDH networks. These two types of transmission families provide transportation layer functionality with different capabilities.
There currently exist several common topologies for these types of transmission products.                1. Point to point: In a point-to-point connection, two switches are directly connected via a transmission line.        2. Chain: In a chain connection, multiple Add Drop Multiplexers (ADMs) are connected in serial fashion. One application of a chain network is dropping Primary Rate Interfaces (PRIs) at several serial points.        3. Ring: In a ring network topology, multiple switches are connected using multiple ADMs connected in a ring formation. Applications of a ring network include Metropolitan Area Networks (MANs) and Wide Area Networks (WANs).        4. Star: In a start network topology, multiple switches are connected to a main switch via a plurality of ADMs and a main ADM.        
The ring and star network topologies are the most common. Examples of these two topologies are presented below.
A block diagram illustrating a prior art network having a ring topology wherein multiple ADMs make up the ring is shown in FIG. 1. The network, generally referenced 10, comprises class-5 switches 14, an SDH ring topology network 12 made up of a plurality of ADMs 18, and a class-4 switch 16. The ADM devices 18 in the SDH ring network 12 are connected to each other via optical fiber connections 20, as indicated by the dotted arrows. Each Class-5 switch 14 is connected on the network side to an ADM device 18 via a one or more copper TDM transmission lines (e.g., N×E1 lines) as indicated by the solid arrows. On the user side, the Class-5 switches are connected to telephones 22 via local loop lines 30 or to PBX equipment 24 located in enterprises via E1 transmission facilities 26.
The connection to the upper hierarchy levels is via one of the ADM transmission products which is connected to a Class-5 switch via one or more E1 lines 34, which in turn is connected to a Class-4 switch 16 via one or more E1/E3 or OC-3/OC-12 facilities 32.
Note that in this example and throughout this document, the transmission lines and telco networks shown are intended as examples only. Thus, the E1 lines may be replaced by any other suitable TDM type transmission facility including, but not limited to, T1, T3, E1, E3, OC-3, OC-12, STM-1, STM-4, etc. Similarly, the European SDH network and E1/E3 lines can be replaced with the American SONET and T1/T3 standards.
A block diagram illustrating a prior art network having a star topology wherein a main ADM is connected to a plurality of ADMs is shown in FIG. 2. The network, generally referenced 40, comprises class-5 switches 44, an SDH star topology network 50 made up of a plurality of ADMs 51, and a class-4 switch 42. The ADM devices 51 in the SDH star network 50 are connected to each other via optical fiber connections 52, as indicated by the dotted arrows. Each Class-5 switch 44 is connected on the network side to an ADM device 51 via a one or more copper TDM lines (e.g., N×E1 lines) as indicated by the solid arrows 54. On the user side, the Class-5 switches are connected to telephones 62 via local loop lines 60 or to PBX equipment 56 located in enterprises via E1 transmission facilities 58.
The connection to the upper hierarchy levels is via one of the ADM transmission products which is connected to a Class-5 switch via one or more E1 lines 48, which in turn is connected to a Class-4 switch 42 via one or more E1/E3 facilities 46.
Note that, as described above, the E1 lines may be replaced by any other suitable TDM type transmission facility including T1, T3, E3, etc. Similarly, the European SDH network and E1/E3 lines can be replaced with the American SONET and T1/T3 standards.
A significant disadvantage is that traditionally, transmission products are expensive, particularly in terms of management and maintenance aspects. The main reason for the high costs of management and maintenance of transmission equipment is the lack of flexibility of both the equipment and the topology. In addition, most transmission equipment is characterized by non-trivial configuration and maintenance procedures. This makes networks with large numbers of transmission equipment products difficult to install, configure and maintain requiring skilled crafts that are specially trained to operate and maintain the equipment.
On the other hand, transmission equipment today provides high quality connections utilizing bandwidth reservation. In addition, most equipment has fast fault detection and high fault tolerance capabilities.
Historically, telecommunications companies (i.e. PTTs) provided voice services only. Today, virtually every telecommunication company around the world provides not only voice services but data services as well. Some telcos have been providing both voice and data services for many years already while others are only beginning now. Due to historical reasons, the PTTs that provide data voice services operate two separate networks: one for voice and the other for data. FIGS. 1 and 2 described above, presented examples of voice networks only.
An example of current separate data and voice networks will now be described. A block diagram illustrating a prior art telco network comprising separate voice and data networks are shown in FIG. 3. The network, generally referenced 70, comprises separate voice network 72 and data network 74. The voice network may have any suitable topology such as ring, star etc.
Voice from home telephones 84 is carried by local loop lines to the user side to Class-5 switches 78. In the enterprise 82, voice is handled by PBXs connected to the switch via copper TDM facilities, e.g., E1 lines. The enterprise data connection is through the voice network. A router is connected to the user side of the nearest Class-5 switch via one or more TDM facilities, e.g., E1, T1, etc. Alternatively, the router may have a direct connection 83 to the voice network via optical fiber, e.g., OC-3, through an ADM. In addition, the router may be directly connected to the data network via an optical fiber connection 85 (e.g., OC-3) to an ATM or FR switch connected to the data network.
The network side of the Class-5 switches is connected to ADMs 80 via one or more E1 lines. A connection to upper levels in the hierarchy is made through the Class-4 switch 76 connected to a Class-5 switch via higher capacity E3 transmission lines.
On the data side, as an example, xDSL subscribers are connected to a Digital Subscriber Line Access Multiplexer (DSLAM) 88. In particular, a Small Office/Home Office (SOHO) environment 90 comprises a PBX 94 and a LAN 98 connected to a router 96. The PBX and router are connected to a Network Termination Unit (NTU) 92 which is connected to the DSLAM via copper. Similarly, a home environment comprises a telephone 100 and workstation 102 connected to a NTU 104. The NTU 104 is also coupled to a port in the DSLAM 88 via copper.
The data portion of the signal is separated from the data, using splitters or an equivalent thereto. Data traffic is passed on to a data switch 86 such as ATM or Frame Relay (FR) which is connected to the data network 74. Voice traffic is directed to a Class-5 switch via a TDM transmission facility, e.g., T1, E1, etc. which feeds the voice traffic to the voice network 72.
There is, however, a big disadvantage with the configuration described above. The disadvantage is that the telecommunications company must build, install, operate, maintain and manage two different networks. The equipment used is different for each type of network. Each type of network requires separate specialized switching and transmission facility equipment and the trained craft personnel to build, operate and manage the two networks. The cost to telecommunications companies for building and maintaining two separate networks for voice and data can be enormous. As is the case in most parts of the world, the demand for data services is increasing at a fast rate. This is largely due to the explosive growth of the Internet including the use of the web, email and file transfer. It is also due to more and more work being done electronically in the workplace rather than on paper with the resultant increase in business-to-business data traffic. The demand for voice traffic is also increasing as the number of users of personal communications devices increases. The number of users such devices which comprise, for example, cellular telephones, beepers, etc. is increasing each year. In addition, many third world countries are beginning to modernize their aging communications infrastructures by replacing outdated systems and/or installing new systems where none previously existed.
Thus, there is a need for a solution that will enable the convergence of both voice and data networks into a single network. This would permit PTTs to provide voice and data services at greatly reduced cost. In addition, a combined network would allow PTTs to provide new services to end users.